Caroni Arena Pump

ARENA DAM
The Arena Dam is located on the Arena River in the north central
region of Trinidad (Refer To Figure 1.0), it forms a 35,000 acre feet
reservoir which serves as the main raw water storage facility for Trinidad,
augmenting the dry season. Water from the Arena is impounded during the
wet season for release systematically during the dry season .The Arena River
provides about 40% of the water needed to fill the reservoir , the remainder
is obtained from the Tumpuna River. A weir is located downstream of the
confluence of the Arena and Tumpuna Rivers backs water up the Arena River
channel to the dam toe .Consequently During the wet season a pumping
station at the base of the dam pumps water back into the reservoir and
During the dry season water is released through the outlet works and flows
down the Arena and Tumpuna Rivers to the Caroni River an there it is
withdrawn for water treatment. This system allow for an approximate 75
million gallons per day of treated drinking water year round about half of the
island supply.
The
earth fill embankment is approximately 1.6 million cubic yards and has a
crest elevation of about 80 feet above the original streambed (Refer to
Figure 2.0 & 3.0). The upstream sloping core is composed of dispersed
clay, and the shells are composed of compacted fine sand and silty fine sand.
The Arena Dam is built upon deep, stiff, fissured clay soil interbedded with
sand .The Dam is located approximately 12 miles from the El Pilar Fault (a
major Caribbean fault with seismic activity which can be compared to that of
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the San Andres Fault).At the dam Site, a flood plain approximately 800 feet
wide lies at an elevation of an approximate 73 feet above the mean sea
level. This flood plain is underlain by up to 50 feet of alluvium. Prior to
construction, the Arena River flowed in a channel approximately 20 feet deep
in the flood plain. The reservoir consist of rolling hills with relief generally
ranging from 150 feet to 200 feet.
Figure 1.0 showing the vicintiy map
Figure 2.0 showing Maximum Dam Section
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Figure 3.0 showing the outlet conduit profile
PUMPED STORAGE CONCEPT
The principle governing the pumped storage concept is fairly simple, it

utilized gravitational potential to store energy .In perspective there are two
bodies of water, one located at a higher elevation than the other, and a
system of tunnels and piping connects them both. When the demand is low
(referred to as the off peak time) and electricity is cheap the plant uses
energy to pump water from the lower reservoir to the upper reservoir (Refer
To Figure 5.0). Subsequently, when Demand is high (known as the Peak Time
) and electricity is more expensive water from the elevated reservoir is

released back into the lower reservoir through the same system of pipes , at
this point turbines as they would normally in a traditional hydroelectric plant
generates electricity (Refer To Figure 4.0) . The system is mainly housed
within man made caverns inside mountains to reduce the environmental
impacts. This type of plant actually has a net use of energy, the advantage
come from the fact that once the facility is operational it can respond quickly
to energy demands. Nearly all facilities use the height difference between
the two reservoirs or natural bodies of water, however there is a slight
difference , a pure pumped storage plant just shifts the water between
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the reservoirs while the pump-back approach is a combination of pumped

storage and conventional hydroelectric plants that use a natural steam-flow.
When taking into account evaporation losses from the exposed water surface
and conversion loses, 70 to 80 percent of the electrical energy used to pump
the water form to lower reservoir to the higher reservoir can be regained
.This technique is currently one of the most effective means of storing large
amounts of electrical energy however capital cost and the appropriate
geography are to be taken into careful consideration.
Figure 4.0 showing the generation of electricity when demand is high .
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Figure 5.0 shows the storage of energy by pumping water to elevated reservoir
WATER TURBINES
A turbine extracts energy from a fluid which possesses high head .In
general there are two types, reaction and impulse, the difference lies in the
manner of head conversion. In the reaction turbine, the fluid fills the blade
passages, and the head change or pressure drop occurs within the impeller.
Reaction Designs are of the radial flow, mixed flow and axial flow types and
are basically dynamic devices designed to convert the high energy fluid to a
form of momentum .An impulse turbine first converts the high head through
a nozzle into a high velocity jet, which then strikes the blades at one position
as they pass by. The impeller passages are not fluid filled, and the jet flow
past the blades is basically at constant pressure.
REACTION TURBINES
Newtons third law is used to describe the transfer of energy for

reaction turbine. Reaction turbines are low head, high flow devices, the flow
is opposite that in a pump entering at the larger diameter section and
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discharging through the eye after giving up most of its energy to the impeller
.The first inward flow turbine was built by James B. Francis an now all radial
or mixed flow designs are now called Francis turbines however ,at lower
heads a turbine can be designed with only axial flow which is termed as a
propeller turbine , the propeller may either be fixed blade or adjustable
which is known as the Kaplan turbine .
THE FRANCIS TURBINE

These are adaptable to varying heads and flows and may be run in
reverse as a pump such as on a pumped storage set up. They operate in a
water head from 10 to 650 meters and are normally used for electrical power
production, the speed range of the turbine is from 83 to 1000 rpm. These
turbines are most time mounted with the shaft vertical to keep water away
from the attached generator and to accommodate installation and
maintenance access to it and the turbine. The turbine is noted to be an
inward flow device as said before with water entering around the periphery
and moving to the center before exhausting .the rotor is contained in a
casing that spreads the flow and pressure evenly around the periphery.
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Figure 6.0 shows a typical large Francis turbine in which water is fed radially to
the runner from guide vanes which are disposed around the full circumference
THE KAPLAN TYPE TURBINE

The Kaplan turbine is a pure reaction turbine, the main feature is that
all the flow energy and pressure is exhausted over the rotor and not in the
supply nozzle .Kaplan turbines are more suited for low pressure heads and
large flow rates such as on dams and tidal barrage schemes.
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Figure 7.0 Shows details of a large Kaplan turbine through which the water flow
is essentially axial.
IMPULSE TURBINES
The impulse turbine utilizes the concept of Newtons Second law and is
suitable in applications requiring high head and relatively low power. Impulse
turbines changes the direction of flow of a high velocity fluid, the resulting
impulse then spins the turbine and leaves the fluid flow with a lower kinetic
energy than its initial. Before reaching the turbine the fluids pressure head is
changed to velocity head by accelerating the fluid with a nozzle, because of
this these turbines do not require a pressure casement around the rotor since
the fluid jet is created by the nozzle before reaching the blade on the rotor
which normally has an elliptical split-cup shape .the Pelton wheel is an
example of an impulse turbine and was named after Lester A. Pelton who
produced the first efficient design.
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Figure 8.0 shows a typical design of A Pelton Wheel
DIFFERENCE BETWEEN IMPULSE AND REACTION TURBINE
N.
O
1.
Impulse Turbine
Reaction Turbine
The fluid flows through

the nozzle and
impinges on the
moving
The fluid first flows

through the guide
mechanism and then
through the moving
blades
The fluid glides over
the moving vanes with
pressure and kinetic
energy
He fluid pressure is
reduced during its flow
through the moving
blades
The blades are not
symmetrical
2.
The fluid impinges on

the buckets with kinetic
energy
3.
The fluid may or may

not be admitted over
the whole
circumference
The blades are
symmetrical
4.
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REFERENCES
Websites
https://mospace.umsystem.edu/xmlui/bitstream/handle/10355/34526/P
%200651-%20Design%20and%20Peformance%20of%20Arena%20Dam.pdf?
sequence=1
http://www.technologystudent.com/energy1/pstr1.htm
http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity
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http://www.mech.uq.edu.au/courses/mech7350/lecture-notes-inpdf/mech7350-10-hydraulic-turbines.pdf
http://www.freestudy.co.uk/fluid%20mechanics/t8a203.pdf
http://large.stanford.edu/courses/2010/ph240/boysen2/
Books
Fluid Mechanics Frank M White 4th edition
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ARENA DAM

Figure 1.0 showing the vicintiy map

Figure 2.0 showing Maximum Dam Section

Figure 3.0 showing the outlet conduit profile

PUMPED STORAGE CONCEPT

The principle governing the pumped storage concept is fairly simple, it

) and electricity is more expensive water from the elevated reservoir is

the reservoirs while the pump-back approach is a combination of pumped

Figure 4.0 showing the generation of electricity when demand is high .

Newtons third law is used to describe the transfer of energy for

THE FRANCIS TURBINE

THE KAPLAN TYPE TURBINE

Figure 8.0 shows a typical design of A Pelton Wheel

DIFFERENCE BETWEEN IMPULSE AND REACTION TURBINE

The fluid flows through

The fluid first flows

The fluid impinges on

The fluid may or may

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